A number of vehicles are equipped with car navigation systems using GPS (Global Positioning Systems) systems to derive the location of the vehicle from signals transmitted by satellites. A car navigation system also includes a display screen and a database providing map data used within the system to generate maps of roads within the region in which the vehicle is operating. The position data and the map data are used together to derive the position of the vehicle on a road, which is then displayed, along with surrounding roads, on the display screen. The map data is generally provided to the system in the form of read-only data recorded on one or more compact discs.
The patent literature includes a number of patents describing methods for adding traffic data to the information displayed by a car navigation system on a real time basis. For example, U.S. Pat. No. 5,699,056 describes a traffic information system including a number of vehicles in radio communication with a center. In one embodiment of the system, the presence or absence of a traffic jam is determined within the center based on only information automatically transmitted to the center from apparatus on the vehicles. A car navigation system on each of the vehicles performs as a position sensor, giving the position of the vehicle. Each of the vehicles is connected to the center through a radio network including a number of repeaters located throughout a region. The information transmitted to the center includes at least a vehicle identifier, time data, and position data. An information processor in the on-board apparatus in each vehicle transmits this information at least twice at suitable time intervals. Using data transmitted from a number of vehicles, the center calculates an average vehicle speed for each block forming a portion of a road within a region supervised by the center and determines that a traffic jam has occurred within the block if the average vehicle speed is less than a predetermined value. The number of vehicles within the block may also be considered in this determination, and the average vehicle speed may be additionally used to determine the severity of a traffic jam in a block. Information identifying the traffic jam and its location is transmitted from the center to vehicles, to be displayed at corresponding locations on the displayed maps.
Other versions of the traffic information system of U.S. Pat. No. 5,699,056 include the use of instrumentation on the vehicles to determine road and weather conditions and to measure the shapes of other vehicles, so that information that is more extensive is transmitted to the center and returned to the vehicles. What is needed is a traffic information system providing communications among a very large number of vehicles within a large region and a center without a need to build a specialized radio network including a large number of repeaters to cover the distances involved. Additionally, what is needed is a communication system operating in an efficient manner so that thousands of vehicles can communicate with a center without jamming the associated radio frequencies.
U.S. Pat. App. Pub. No. 2001/0029425 describes a system providing vehicle guidance by a central traffic unit maintaining a perpetually updated database of travel times for all sections of roads. Mobile guidance units within the vehicles include mobile cell phone handset units located in mounting receptacles and communicatively linked to the central traffic unit computer server. To detect a bottleneck situation as it arises, and to estimate travel times for a section of road, the central traffic unit maintains a list of vehicles that have recently exited that section. If the times those vehicles have spent in the section differ substantially from a regular travel time stored in a database, the central traffic unit uses statistical tools for forecasting a future travel time along the section.
In response to a request from a driver for a route update from his present position to a desired destination, communicated via mobile phone to the central traffic unit, the central traffic unit calculates the desired fastest route by utilizing both the regular travel times along segments of the roads and predicted current travel times calculated using information collected from the vehicles. The fastest route is then communicated to the guidance unit for display on a computer screen.
The mobile guidance units within the vehicles passively collect traffic information as they travel. A circuit card within the mobile guidance unit causes the mobile cell phone handset unit to transmit real time position data via a mobile telephone transmission protocol. A client of the guidance system may enter a navigation query via a network service through a voice processor in the central traffic unit. The mobile guidance unit in a vehicle can be used to transmit a request in a PC Internet/WAP software application, with the request being transmitted through a telecommunications network to an Internet/WAP server. The navigation directions are returned by TCP/IP protocol in terms of digital map and text/voice driving instructions. Other potential users and trip planners access the on-line guidance system through Internet browsers, receiving a description of a shortest path solution between starting and destination points.
U.S. Pat. App. Pub. No. 2001/0056325 describes a client navigation system in an automobile that establishes a wireless connection to a navigation server on a computer network, such as the Internet, requesting a route by uploading start and stop specifications. The server calculates an optimal route based on real-time data available on a network and transmits route information to the client navigation system, which interprets the route, interfaces with a local mapping database, and reconstructs the optimal route.
U.S. Pat. No. 5,425,544 describes a method and apparatus for the transfer of traffic information among vehicles and for assisting the navigation of the vehicles. The traffic information is routinely and automatically transmitted between vehicles passing on a highway. The apparatus includes sensors to detect the direction and displacement of the vehicle, a microcomputer to recognize the position of the vehicle by referring the detected direction and displacement to a digitized map; a receiver to receive the passing vehicle's traffic information to be processed by the microcomputer; a transmitter to transmit traffic information to the passing vehicle; and a navigation unit in the microcomputer to generate navigation information. The traffic information transferred among vehicles includes traffic information generated in the vehicles themselves and traffic information received from other vehicles.
Hence, there is a need for a method and system for communicating traffic information between a number of vehicles and a server computer that is novel and efficient without burdening the server that the system is connected to.